Health care institutions, concerned that less than half their workers got flu shots in previous years, are moving for the first time to make the shots mandatory in the face of an expected swine flu pandemic.

Centers for Disease Control and Prevention figures for the 2007-08 flu season, the most recent available, show that just 45.4 percent of U.S. health care workers ages 19 to 64 were immunized against seasonal flu that year. Three British surveys released in recent weeks suggest the same pattern with the novel H1N1 virus, commonly known as the “swine flu” virus.

But Dr. Tom Talbot, a professor at Vanderbilt University School of Medicine, said “there has been a big wave this year” of mandatory vaccination rules, ranging from small doctors’ offices to large medical care and hospital systems.

“A lot of people are leaning [toward mandatory vaccinations], pointing to it as a safety issue, akin to a surgeon refusing to do a scrub before surgery,” he said.